If you live in UK, you've heard this sound many times. At the start of each hour, BBC send a series of 6 tones known as "The Pips".
Tones are divided in two parts, the first one is a series of 5 equal tones that last for 0.1 seconds and mark the 5 seconds preceding a new hour.
Second part represent a single tone, 5 times longer which last for 0.5 seconds and mark the beggining of the new hour. Tone waves are a sine at 1000Hz frequency.

Timing in the era of digital radio is hard to get and reflect the precise hour change, due to the delay in sound processing equipments and broadcasting.
Consider this as a part of the radio history and enjoy it.

Greenwich Time Signal can be heard here or you can download the tone using our widget.